An actuator is used in a railway vehicle, for example, with being interposed between a vehicle body and a truck in order to suppress vibration in a left-right direction relative to an advancing direction of the vehicle body.
JP2010-65797A discloses an actuator including: a telescopic body having a cylinder, a piston inserted into the cylinder to be free to slide, a rod that is inserted into the cylinder and connected to the piston, and a rod side chamber and a piston side chamber defined by the piston within the cylinder; a tank; a first opening/closing valve provided midway in a first passage that connects the rod side chamber to the piston side chamber; a second opening/closing valve provided midway in a second passage that connects the piston side chamber to the tank; a pump that supplies a fluid to the rod side chamber; a motor that drives the pump; an exhaust passage that connects the rod side chamber to the tank; and a variable relief valve provided midway in the exhaust passage.
According to this actuator, a direction of an output thrust is determined by appropriately opening and closing the first opening/closing valve and the second opening/closing valve, whereupon the pump is rotated by the motor at a fixed speed such that the fluid is supplied into the cylinder at a fixed flow rate. Meanwhile, an internal pressure of the cylinder is controlled by adjusting a relief pressure of the variable relief valve, and in so doing, a thrust of a desired magnitude can be output in a desired direction.